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OSPF Database Help

 
 
ccie2k4
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      09-01-2006
Hi, can someone please help me in trying to understand the OSPF
Database. Per my understanding the Database is structured per the
Areas. Each Area will contain LSA's under it. I am confused as to what
LSA's will appear under what area.
For eg:

1. The ASBR Summary LSA in the output below appears only under Area 51
but in other topologies and output I have seen it appear under Area 0
as well.

2. Under the summary LSA I see 172.16.10.4 under the Area 0 section as
well as the Area 51 section? Why is that.





OSPF Router with ID (192.168.2.1) (Process ID 1)

Router Link States (Area 0)

Link ID ADV Router Age Seq#
Checksum Link count
172.16.10.5 172.16.10.5 751 0x8000000F
0x6F9C 1
192.168.1.1 192.168.1.1 540 0x80000012
0x8D3D 1
192.168.2.1 192.168.2.1 543 0x80000016
0x7E46 1
192.168.3.1 192.168.3.1 543 0x80000005
0x9C36 1

Net Link States (Area 0)

Link ID ADV Router Age Seq#
Checksum
172.16.1.2 192.168.2.1 539 0x8000000D
0xCFE8

Summary Net Link States (Area 0)

Link ID ADV Router Age Seq#
Checksum
172.16.10.4 192.168.3.1 617 0x80000001
0xD126
172.16.20.0 192.168.3.1 617 0x80000001
0xA746
172.16.51.1 192.168.2.1 544 0x80000005
0xA832


Router Link States (Area 51)
Link ID ADV Router Age Seq#
Checksum Link count
192.168.2.1 192.168.2.1 585 0x8000000B
0x855 1

Summary Net Link States (Area 51)

Link ID ADV Router Age Seq#
Checksum
172.16.1.0 192.168.2.1 531 0x80000001
0xE22F
172.16.10.4 192.168.2.1 531 0x80000001
0xE215
172.16.20.0 192.168.2.1 531 0x80000001
0xB835

Summary ASB Link States (Area 51)

Link ID ADV Router Age Seq#
Checksum

192.168.1.1 192.168.2.1 531 0x80000001
0x9EC4

Type-5 AS External Link States

Link ID ADV Router Age Seq#
Checksum Tag
11.0.0.0 192.168.1.1 988
0x80000001 0x3FEA 0
12.0.0.0 192.168.1.1 988
0x80000001 0x32F6 0
13.0.0.0 192.168.1.1 988
0x80000001 0x2503 0



In addition say if i look at the sho ip ospf data asbr-summary output
and see that for LSA's appearing under Area 51 it gives the message the
advertising router is not reachable. However I see the route to the
advertising router in my routing table and am able to ping it as well.
Could it be that the area 51 is upstream to the router I am looking at
and hence because its upstream it doesn't make sense to put this
routers LSA in the routing table since that would cause a routing loop
and that is the reason why it says "Adv Router is not-reachable"

 
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ccie2k4
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Posts: n/a
 
      09-06-2006
Can someone please assist. Thanks


ccie2k4 wrote:
> Hi, can someone please help me in trying to understand the OSPF
> Database. Per my understanding the Database is structured per the
> Areas. Each Area will contain LSA's under it. I am confused as to what
> LSA's will appear under what area.
> For eg:
>
> 1. The ASBR Summary LSA in the output below appears only under Area 51
> but in other topologies and output I have seen it appear under Area 0
> as well.
>
> 2. Under the summary LSA I see 172.16.10.4 under the Area 0 section as
> well as the Area 51 section? Why is that.
>
>
>
>
>
> OSPF Router with ID (192.168.2.1) (Process ID 1)
>
> Router Link States (Area 0)
>
> Link ID ADV Router Age Seq#
> Checksum Link count
> 172.16.10.5 172.16.10.5 751 0x8000000F
> 0x6F9C 1
> 192.168.1.1 192.168.1.1 540 0x80000012
> 0x8D3D 1
> 192.168.2.1 192.168.2.1 543 0x80000016
> 0x7E46 1
> 192.168.3.1 192.168.3.1 543 0x80000005
> 0x9C36 1
>
> Net Link States (Area 0)
>
> Link ID ADV Router Age Seq#
> Checksum
> 172.16.1.2 192.168.2.1 539 0x8000000D
> 0xCFE8
>
> Summary Net Link States (Area 0)
>
> Link ID ADV Router Age Seq#
> Checksum
> 172.16.10.4 192.168.3.1 617 0x80000001
> 0xD126
> 172.16.20.0 192.168.3.1 617 0x80000001
> 0xA746
> 172.16.51.1 192.168.2.1 544 0x80000005
> 0xA832
>
>
> Router Link States (Area 51)
> Link ID ADV Router Age Seq#
> Checksum Link count
> 192.168.2.1 192.168.2.1 585 0x8000000B
> 0x855 1
>
> Summary Net Link States (Area 51)
>
> Link ID ADV Router Age Seq#
> Checksum
> 172.16.1.0 192.168.2.1 531 0x80000001
> 0xE22F
> 172.16.10.4 192.168.2.1 531 0x80000001
> 0xE215
> 172.16.20.0 192.168.2.1 531 0x80000001
> 0xB835
>
> Summary ASB Link States (Area 51)
>
> Link ID ADV Router Age Seq#
> Checksum
>
> 192.168.1.1 192.168.2.1 531 0x80000001
> 0x9EC4
>
> Type-5 AS External Link States
>
> Link ID ADV Router Age Seq#
> Checksum Tag
> 11.0.0.0 192.168.1.1 988
> 0x80000001 0x3FEA 0
> 12.0.0.0 192.168.1.1 988
> 0x80000001 0x32F6 0
> 13.0.0.0 192.168.1.1 988
> 0x80000001 0x2503 0
>
>
>
> In addition say if i look at the sho ip ospf data asbr-summary output
> and see that for LSA's appearing under Area 51 it gives the message the
> advertising router is not reachable. However I see the route to the
> advertising router in my routing table and am able to ping it as well.
> Could it be that the area 51 is upstream to the router I am looking at
> and hence because its upstream it doesn't make sense to put this
> routers LSA in the routing table since that would cause a routing loop
> and that is the reason why it says "Adv Router is not-reachable"


 
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